Signal Transduction Pathways
Odorant neuron / Skeletal muscle cellSignal molecule (source) / odorant molecule (from air in the nasal passageway) / acetylcholine (from motor neuron)
Receptor / odorant G-protein-linked receptor / acetylcholine-gated Na+ channel
Transduction pathway members (proteins) / 1. G-protein (especially α-subunit)
2. adenylyl cyclase
3. cAMP-gated Ca2+, Na+ channel
4. Ca2+-gated Cl- channels / 1. voltage-gated Na+ channels (action potential-producing)
2. voltage sensor proteins of T tubules
3. Ca2+ release channels
4. troponin
Second messenger(s) in transduction pathway / cAMP (1st) and Ca2+ (2nd) / Na+ (?) and especially Ca2+
How amplification is achieved in transduction pathway (a few sentences) / An activated G-protein-linked receptor can convert many inactive G-proteins (especially α-subunit) into their active form.
Adenylyl cyclase is an enzyme and can convert many ATP molecules to cAMP.
The cAMP-gated Ca2+,Na+ channel is a channel and many Ca2+ and Na+ ions rush in when it’s open.
The Ca2+-gated Cl- channel is a channel and many Cl- ions rush out when it’s open. / Both voltage-gated channels are channels and many Na+ or Ca2+ ions rush into the cytosol when they are open.
Response (a few sentences)
What does this pathway contribute to this response? / The plasma membrane depolarizes (due to the rushing in of Na+ cations through the cAMP-gated Ca2+,Na+ channels and the rushing out of Cl- anions through the Ca2+-gated Cl- channels) past the threshold level and an action potential travels down the axon to the mitral cell. / When troponin binds Ca2+ cations, it moves tropomyosin so it no longer blocks the myosin binding sites on the actin thin filaments, so the thick filaments can move the thin filaments toward the center of the sarcomere. The muscle contracts!
Signal Transduction Pathways
Signal molecule (source) / epinephrine (from adrenal medulla) / epinephrine (from adrenal medulla)
Receptor / α1-type epinephrine G-protein-linked receptor / β-type epinephrine G-protein-linked receptor
Transduction pathway members (proteins) / 1. G-protein (especially α-subunit)
2. phospholipase C
3. IP3-gated Ca2+ channels on the endoplasmic reticulum (IP3 is inositol triphosphate) and DAG-gated Ca2+ channels in the plasma membrane (DAG is diacylglyceride) / 1. G-protein (especially α-subunit)
2. adenylyl cyclase
3. cAMP-dependent protein kinase A
4. phosphorylase kinase (also needs Ca2+)
5. glycogen phosphorylase
Second messenger(s) in transduction pathway / IP3 and Ca2+ (DAG isn’t usually considered a 2nd messenger since it isn’t water soluble) / cAMP
How amplification is achieved in transduction pathway (a few sentences) / When epinephrine is bound to its α1-type receptors many G-proteins are activated.
Phospholipase C is an enzyme and so can convert many molecules of PIP2 to IP3 and DAG.
The IP3-gated Ca2+ channels and the DAG-gated Ca2+ channels are channels and so many Ca2+ cations can enter while they’re open. / When epinephrine is bound to its β-type receptors many G-proteins are activated.
Adenylyl cyclase is an enzyme and so can convert many molecules of ATP to cAMP.
Each enzyme in the phosphorylation cascade (3 - 5 above) amplifies the signal because enzymes can convert many molecules of substrate to product.
Response (a few sentences) / Main response is the phosphorolysis of glycogen to glucose and its release into the blood.
The enzyme that activates glycogen phosphorylase needs Ca2+ to be fully active and this pathway provides the Ca2+. / Main response is the phosphorolysis of glycogen to glucose and its release into the blood.
Glycogen phosphorylase must have a phosphoryl group added to be active and this pathway provides the phosphoryl group.